1. Field of the Invention
The present invention relates to building construction and the like, and particularly to precast, reinforced concrete construction elements with pre-stressing connectors for post-tensioning of beam-column joints.
2. Description of the Related Art
In construction of buildings or the like, beams are used to span between upstanding members, typically referred to as columns. The beams are adapted to carry loads, such as concrete floors and the like. Prior to advances made in the usage of reinforced concrete, beams and columns were typically made from steel, particularly due to its enhanced load bearing characteristics per unit weight. In addition to simple construction, in which steel beams (typically in the form of I-beams) are erected to span between columns and carry the designed loads, external post-tensioning of the steel beams may be added. External tensioning is accomplished by suitable location of the columns and by tensioning the beam to span therebetween.
Developments in the field of reinforced concrete has allowed for construction using reinforced concrete beams and columns, replacing (or used in addition to) steel construction elements. Unlike steel beams, reinforced concrete beams may be internally post-stressed or pre-stressed. To construct such concrete beams, a network of steel cables extends through and along the length of the beam. If the beam is to be pre-stressed, the cables are positioned in a mold, with the mold having steel plates at its ends. Hydraulic jacks or the like are then used to tension the cables in the mold. Thereafter, concrete is poured into the mold between the end plates to encase the cable network. After the concrete has sufficiently hardened, the tension cables are secured to the end plates and released to place the concrete beam in compression.
In post-stressing, the network of cables is positioned and concrete is poured thereabout, either in a mold or in situ to encase the cables. End plates are attached to the concrete beam, with certain cables extending therethrough. After the concrete is sufficiently hardened, the cables are tensioned and thereafter secured to the end plates and released to place the concrete beam in compression. The pre-stressing and post-stressing techniques are effective in enhancing the load bearing characteristics of the beam.
FIG. 2 illustrates a typical conventional pre-stressed construction element 114, in the form of a beam spanning between a pair of upstanding columns 112. To provide for connection of the beam 114 between columns 112, each column 112 has a connection plate 118 projecting therefrom. The exemplary conventional pre-stressed beam 114 of FIG. 2 is in the form of an I-beam, having a web 120 interconnected between two spaced flanges 122. To enhance the strength of the beam 114 so that relatively smaller and lighter beams may be used to support a given projected load, at least one tendon 124 extends longitudinally alongside the beam 114. Tendons 124 are adapted to be tensioned by placing the beam 114 under compressive forces, thus pre-stressing beam 114. Such tendons 124 are typically in the form of steel cables having a number of strands.
Although pre-stressing of beams, such as in beam 114, enhances the load bearing characteristics of the beam itself, such pre-stressing does not aid in enhancing the properties of the connections between the beams and the columns. It would be particularly desirable to be able to provide enhancement and reinforcement for beam-column connections to mitigate damage caused by earthquakes, building collapse and the like. Further, there are major concerns with regard to precast, reinforced concrete buildings due to their vulnerability to progressive collapse during the event of column loss/damage due to blast loads. This vulnerability is mainly due to the weakness of the connections in precast, reinforced concrete frames, especially when a beam-column joint moves downward because of the removal/damage of the column connected to the joint. It would obviously be desirable to be able to improve the beam-column joints/connections. Thus, precast, reinforced concrete construction elements with pre-stressing connectors solving the aforementioned problems is desired.